1. Field of the Invention
The present invention relates to a double-acting piston engine having a pair of cylinders positioned on each side of a crankshaft and confronting each other and a pair of pistons slidably disposed in the respective cylinders and connected to each other.
2. Description of the Prior Art
One conventional double-acting piston engine is disclosed in Japanese patent publication No. 51-35645 or Japanese laid-open patent publication No. 49-63806. The disclosed double-acting piston engine comprises a joint interconnecting a pair of pistons and having an internal gear and a crankshaft having external pinions concentric with crankpins and held in mesh with the internal gear. Reciprocating movement of the pistons is transmitted through the internal gear and the external pinions to the crankshaft, thus rotating the crankshaft about its own axis.
The prior double-acting piston engine may be reduced in size and can produce large output power while causing reduced vibration.
However, if the double-acting piston engine is reduced in size, then the power transmitting mechanism that is composed of the internal gear and the external pinions for converting reciprocating movement of the pistons to rotary movement of the crankshaft is also reduced in size and hence mechanical strength.
The power transmitting mechanism is lubricated by lubricating oil which is supplied through lubricating holes defined from the crankshaft to the crankpins. The mechanical strength of the crankshaft tends to be reduced because of the lubricating holes.